1. Field of the Invention
The present invention relates to a fluid bearing apparatus, more particularly, to a fluid bearing apparatus wherein the clearance between the surface of a thrust bearing and a rotary shaft can be adjusted by making the thrust bearing movable with respect to an end portion of the rotary shaft.
2. Description of the Related Art
FIG. 1 is a sectional view of an embodiment of a fluid bearing apparatus according to a conventional art.
As shown in the drawing, a thrust bearing 50 is installed at an end of a through hole 25 in a sleeve 20. A rotary shaft 30 is inserted into the sleeve 20. A lower end portion of the shaft 30 faces the thrust bearing 50 which supports a vertical thrust load of the shaft 30. A first dynamic pressure generating groove 50a is formed on the upper surface of the thrust bearing 50. The sleeve 20 is fastened to the thrust bearing 50 with a clamp screw or the like. In the sleeve 20, an air vent 20a is formed to ventilate air between the thrust bearing 50 and the shaft 30. Furthermore, a second dynamic pressure generating groove 30a having a herringbone shape is formed on the outer surface of the shaft 30 inserted into the through hole 25, or the inner peripheral surface of the sleeve 20.
When the shaft 30 is revolved, a clearance is created between the thrust bearing 50 and the lower end portion of the rotary shaft 30. When the clearance is wide, the shaft 30 may be vibrated and oscillated. On the other hand, when the clearance is narrow, a high pressure and heat are generated between the lower end portion of the shaft 30 and the thrust bearing 50. Heat causes the thrust bearing 50 and the shaft 30 to fuse with each other. As a result, the revolution of the shaft 30 may be stopped. For this reason, the clearance between the lower end portion of the shaft 30 and the thrust bearing 50 is a critical factor for high accuracy and high speed revolution of the fluid bearing apparatus.
In the conventional fluid bearing apparatus, the clearance is extremely narrow in the range of several to several dozen .mu.m. Accordingly, an actual clearance during the operation of the bearing apparatus may be different from an originally designed clearance between the surface of the thrust bearing 50 and the lower end portion of the shaft 30, due to a variation in the length of the shaft 30 or in the depth of the dynamic pressure generating groove. In addition, friction and abrasion of the thrust bearing and the shaft in repeatedly using the bearing apparatus cause the clearance between the bearing and the shaft to be wider than the originally designed clearance. Therefore, an adjustment in the clearance between the thrust bearing and the shaft for using the bearing apparatus is needed.
However, there is a disadvantage that after the thrust bearing and the shaft are assembled, it is impossible to adjust the clearance between the thrust bearing and the shaft in the fluid bearing apparatus according to the embodiment using the conventional art.